1. Field of the Invention
This invention relates in general to magnetic sensors for reading information signals stored on a magnetic medium and, more particularly, to an improved magnetoresistive read sensor which utilizes a dual spin valve structure.
2. Description of the Prior Art
The prior art discloses a magnetic read transducer referred to as a Magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at great linear densities. An MR sensor detects magnetic field signals through the resistance changes of a read element fabricated of a magnetic material as a function of the strength and direction of magnetic flux being sensed by the read element. More recently, a different, more pronounced magnetoresistive effect has been described in which the change in resistance of a layered magnetic sensor is attributed to the spin-dependent transmission of the conduction electrons between magnetic layers through a nonmagnetic layer and the accompanying spin-dependent scattering. This magnetoresistive effect is sometimes referred to as the "giant magnetoresistive" effect, or, simply, "giant magnetoresistance."
Commonly assigned U.S. Pat. No. 5,206,590 discloses an MR sensor in which the resistance between two uncoupled ferromagnetic layers separated by a nonmagnetic layer is observed to vary as the cosine of the angle between the magnetizations of the two layers and in which the direction of magnetization of one of the ferromagnetic layers is fixed. This MR sensor is referred to as a "spin valve." and is based on the giant magnetoresistive effect.
Commonly assigned U.S. Pat. No. 5,287,238 describes an MR sensor having a multilayered dual spin valve structure. This structure includes two outer layers of ferromagnetic material wherein the magnetism has a fixed orientation, and an intermediate layer of ferromagnetic material wherein the magnetization is free to rotate in response to an externally applied magnetic field.